The present invention relates to assays for an analyte, such as an antigen, in a liquid sample, such as body fluid. More particularly, the present invention relates to a method and device for the detection of an analyte in a body fluid using a lateral flow test cell containing a novel biphasic chromatographic substrate.
Many types of ligand-receptor assays have been used to detect the presence of various substances in body fluids such as urine or blood. These assays typically involve antigen-antibody reactions, synthetic conjugates comprising enzymatic, fluorescent, or visually observable tags, and specially designed reactor chambers. In most of these assays, there is a receptor (e.g. an antibody) which is specific for the selected antigen, and a means for detecting the presence and/or amount of the antigen-antibody reaction product. Most current tests are designed to make a quantitative determination, but in many circumstances all that is required is a positive/negative indication. Examples of such qualitative assays include blood typing, pregnancy testing and many types of urinalysis. For these tests, visually observable indicia such as the presence of agglutination or a color change are preferred.
The positive/negative assays must be very sensitive because of the often small concentration of the ligand of interest in the test fluid. False positives can be troublesome, particularly with agglutination and other rapid detection methods such as dipstick and color change tests. Because of these problems, sandwich assays and other sensitive detection methods which use metal sols or other types of colored particles have been developed. These techniques have not solved all of the problems encountered in these rapid detection methods, however. It is an object of the present invention to provide an improved detection device and method having greater sensitivity and discrimination for analytes of interest. Another object of the invention is to provide an assay device which is simpler to manufacture.